Wireless networks allow users to use mobile devices, such as cellular telephones and personal digital assistants (PDAs), for example, to communicate over a wireless link with cells, also commonly referred to as base stations. Each cell is in communication with a mobile switching center (MSC) via a wired link, such as a T1 line, for example, or via a wireless link, such as a microwave frequency link, for example. The mobile devices communicate with the cell, which, in turn, communicates with the MSC. The MSC establishes the communication link between the mobile user and the party that called the mobile user, or the party that was called by the mobile user.
Each MSC has a database known as a home location register (HLR) and a database known as visitor location register (VLR). The HLR is the main database of permanent subscriber information for a mobile network. The HLR is maintained by the subscriber's home carrier (or the network operator where the user initiated the call) and contains user information such as the user's residence address, account status, and certain preferences. The HLR interacts with the MSC, which performs the switching functions needed for call control and processing. The MSC also serves as a point-of-access to the Public Switched Telephone Network (PSTN). The VLR maintains temporary user information, such as the user's current location, to manage requests from subscribers who are out of the area covered by their home system.
When a mobile user initiates a call, a cell in the area where the call was initiated contacts the MSC with which the cell communicates. The MSC switching equipment then determines whether or not the call is coming from the mobile device's home area. If the user is out of the home area, the area VLR causes the MSC handling the call to send out a request for information required to process the call. The MSC handling the call analyzes the HLR identified by the call, and then relays to the appropriate MSC, which in turn updates the home VLR. The home MSC then sends routing information back to the MSC handling the call, which allows it to find the cell where the call originated, and ultimately, the mobile device that initiated the call.
In order to find the mobile device, the MSC sends out a paging request to sets of cells that are in communication with the MSC. Because there are typically a large number of cells associated with each MSC, the MSC attempts to locate the mobile device by sending out paging signals. Once the MSC locates the cell serving the mobile device, the location of the mobile device is updated in the HLR of the home MSC. If the mobile device is not in the home area, a record is also created in the VLR of the out-of-area MSC to enable the roaming mobile device to be served by the out-of-area MSC.
Notwithstanding the vast deployment of cells and MSCs, for various reasons, calls continue to be dropped. This can occur for a variety of reasons, such as, for example, a mobile device user may move to a location that is out of range of any cell, the mobile device may be transmitting at too low of a power level, a physical barrier (e.g., a traffic tunnel) may exist between the mobile device user and the cell that absorbs the signal of the cell and/or of the mobile device, etc. When a call is dropped, although the MSC that is enabling the communication between the parties, neither the called nor the calling party is provided with closure of the conversation. Typically, one of the parties will later attempt to contact the other party to finish the conversation. The party who was not dropped during the call, remains in contact with the network. If the party who was not dropped were provided with the opportunity to leave a voice mail message for the dropped party, there would be closure to the conversation.
Accordingly, a need exists for a cellular network feature that would enable a party to leave a voice mail message for a mobile device user in the event that the mobile device user is dropped during a call.